I voted YANBU. But.... I went NC with my mum many years ago. She is mentally ill.
From the account of my uncle on my mum's side (who is a bit loopy himself) and of my aunty on my dad's side, my mum was a decent person before an accident with a powerdrill that led to a brain haemorrhage.
My older brother (I wasn't born until around 8 years later) was around 18 months old when my mum, post-powerdrill accident, fell to the floor when an aneurysm in her head exploded. The doctors drained the blood from her head and eased the pressure on her brain before it could kill her, unfortunately substantial brain damage had already occurred from the pressure and the doctors told my uncle that she would not be the sister he grew up with and will not be able to differentiate between right and wrong.
From then on, she had two more children, one of whom died at just 2 weeks old, and then me. Obviously I never knew her pre-brain bleed, but suffice to say my upbringing was awful. She nearly destroyed me. There's a chance that had she not have had a brain haemorrhage years prior, she would have not been the nasty witch she became, but there is no way for me to know for sure. I didn't want to go NC with her, as I hate how fractured families become after cutting people off.
I had to go NC with her because she was on a path to completely ruining my life.
TL;DR Generally YANBU, but sometimes needs must.